It is well known that multi-stage compressor rotor disks for gas turbine engines are joined together into rotor spools by welding or bolting adjacent disks. Certain prior art rotors were attached by locating the holes in the disks and bolting the adjacent disks through the holes. For example, U.S. Pat. No. 3,249,293 granted to B. L. Koff on May 3, 1966, U.S. Pat. No. 3,597,110 granted to R. J. Corsmeier on Aug. 3, 1969, and U.S. Pat. No. 4,310,286 granted to G.P. Peters, et al on Jan. 12, 1982 disclose different arrangements for attaching adjacent rotors by locating the bolt hole in the rim of the disk.
Obviously, the bolt holes in the disk or rim of the disk present a stress concentration problem and result in low fatigue life of the assembly. To avoid locating the bolt holes in the blade load carrying portion of the disks, an overhung flange at the rim of the disks was resorted to. For example, U.S. Pat. No. 3,765,795 granted to B. L. Koff on Oct. 16, 1973 and U.S. Pat. No. 3,688,371 granted to B. L. Koff on Sep. 5, 1972 disclose overhung flanges for attaching adjacent rotors.
Obviously, better fatigue life can be achieved by moving the hole away from the disk where the stresses are lower. In certain embodiments this affords the opportunity to shield the flange location by the use of scallops. However, the offset between the flange and the disk web required to obtain access to the bolt puts a large bending load into the web. One method of reducing the bending stress in the web is by offsetting the disk rim to let the blade load counter the bolt load. But, as is apparent to one skilled in this art, the offset adds weight to the disk and the larger the offset required, it follows, that the heavier the disk becomes.
We have found that we can reduce the offset by incorporating a slotted flange that requires the minimal of space and thereby reducing the weight of the rotor when compared to heretofore known designs.